1. Field of the Invention
The present invention relates to over-the-wire catheters and particularly, to rapid exchange and perfusion catheters.
2. Description of the Prior Art
This description of art is not intended to constitute an admission that any patent, publication or other information referred to is "prior art" with respect to this invention, unless specifically designated as such. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 C.F.R. .sctn.1.56 exists.
The technique of eliminating a vascular stenosis by dilating a balloon on a catheter placed within the stenosis was developed by Dr. Andreas Gruntzig. The first marketable catheters for angioplasty were "fixed wire" catheters, in which a core or guide wire was fixed within the catheter to stiffen it so that it could be pushed into position in the vascular system.
Dr. John Simpson and Dr. Edward Robert subsequently developed an "over-the-wire" catheter in which a guidewire was slidably placed within a lumen of the catheter. The guidewire lumen passed from the distal end of the catheter through the balloon to the proximal end of the catheter. This system provided reasonably easy placement of the catheter because the small, flexible guidewire was first positioned beyond the stenosis and the catheter was then slid into place over it. Such over-the-wire catheters are generally coaxial (the guidewire lumen is centered within the inflation lumen) or biaxial or bilumen (the guidewire lumen is parallel to the inflation lumen). Biaxial versions generally slide better over the guidewire than coaxial versions.
More recently, "rapid exchange" catheters have been developed with shorter guidewire lumens passing from the distal end of the catheter through the balloon and opening to the exterior of the catheter somewhere proximal to the balloon; they make catheter exchange over the guidewire easier to accomplish.
Various versions of rapid exchange catheters, either coaxial or biaxial, are shown in the following patents: U.S. Pat. No. 4,762,129 issued to Bonzel, U.S. Pat. Nos. 5,040,548 and 5,061,273 issued to Yock, U.S. Pat. No. 4,748,982 issued to Horzewski, et al., U.S. Pat. No. 4,988,356 issued to Crittenden and U.S. Pat. No. 5,135,532 issued to Kramer. In the Horzewski and Crittenden device, the guidewire lumen contains a slit extending its length (except where it passes through the balloon) so that the guidewire can be removed from the lumen through the slit at a point immediately proximal to the balloon. Examples of rapid exchange catheters on the market are ACS' Alpha.TM. catheter, ACS' RX.TM. catheter, Schneider's Piccolino.TM. and SciMed's Express.TM. catheter.
Although the above catheters have significantly improved and streamlined the angioplasty process, they still leave room for improvement. For example, visualizing the location of the catheter and the guidewire during fluoroscopy is critical during the process of dilatation in order to properly place the guidewire initially, and in order to place and hold the balloon within the stenosis. As a result, the balloon or adjacent areas of the catheter generally possess a marker band visible under fluoroscopy. The guidewire itself, usually made of stainless steel, is visible under fluoroscopy. However, in the above catheters, because a guidewire lumen surrounds the guidewire, and the balloon (as well as the shaft in the case of a coaxial catheter) surrounds the guidewire lumen, the guidewire is not as visible as might be desired.
In addition, plaque buildup in the vessel is usually disposed on one side or another of the vessel wall rather than evenly located around the entire circumference of the wall. In all of the above catheters, the balloon is symmetrically disposed around the guidewire lumen so that it cannot be optimally placed with respect to the plaque build-up. Although catheters with asymmetric balloons have been disclosed, those such as that in Schiff, U.S. Pat. No. 4,576,142, are intra-aortic balloon catheters with fixed-wire systems, or have multiple balloons with internal lumens, such as that in Jang, U.S. Pat. No. 5,071,406.
Catheters have been disclosed having no guide wire lumen at all, at least in the region of the balloon, the guide wire running exterior and parallel to the balloon in use. See, for example, U.S. Pat. No. 5,141,494 issued to Danforth, et al., U.S. Pat. No. 5,046,497 to Millar, and U.S. Pat. No. 4,824,435 to Giesy. A rapid exchange catheter having a guidewire without a lumen parallel to the balloon is also disclosed in U.S. patent application Ser. No. 07/859,769 assigned to the assignee of the present invention. However, it may be difficult to back-load the guidewire into some of these catheters and it is possible that the naked guidewire will dislodge plaque which it encounters, causing possible serious problems in the dilatation process.
Because inflation of the balloon blocks blood flow during dilatation, long dilatation times are usually precluded by dilatation procedures. However, U.S. Pat. Nos. 4,983,167 and 5,019,042 to Sahota and U.S. Pat. No. 5,087,247 to Horn disclose auto-perfusion catheters in which blood is allowed to flow past the balloon even while it is inflated, allowing much longer inflation times. In some cases, apertures in the guidewire lumen passing through the balloon allow blood to circulate through the system while the catheter is in use; in others, the balloon is shaped to define a longitudinal channel through which the blood flows.
In the Sahota patents, there is disclosed a fixed wire catheter having a wire-receiving lumen adjacent to the inflation lumen proximal to the balloon. The lumen receives a wire which can be extended through the stenosis, if needed, after dilation to prevent closure. However, the naked wire still runs past the balloon through the occlusion to directly encounter the stenosis.
Finally, in order to handle well, a catheter has to be sufficiently "pushable" to be pushed into place into the vascular system. At the same time, it requires flexibility so it can be turned through the tortuous vascular system without kinking. Some catheters, such as the present assignee's 14K.TM. catheter and Thruflex.RTM. catheter (shown in U.S. Pat. No. 4,917,666) are over-the-wire catheters having spring coil lumens to improve the pushability of the catheter. At the same time, the spring coil is flexible laterally, with minimized kinking. In the present assignee's Gold X.TM. catheter, a coaxial rapid exchange catheter shown in U.S. patent application Ser. No. 07/919,672 filed Jul. 27, 1992, the outer lumen is similarly made of a spring coil, with a core wire extending through a portion of the coil for added pushability. In the present assignee's Omniflex.TM. catheter (shown generally in U.S. Pat. No. 4,723,936) as sold, a proximal hypotube about 11/2 inches long improves the handling of the catheter, which is otherwise formed of a spring coil.
Other rapid exchange catheters having high pushability are SciMed's Express.TM. catheter, shown in PCT patent application Publication No. WO 92/03178, and ACS' Alpha.TM. catheter (shown in U.S. Pat. No. 5,154,725), a hypotube forms the proximal outer tube of the catheter. This renders the catheter very pushable, at least at the proximal end. In the Express.TM. catheter, a spring coil immediately distal to the hypotube reinforces the lumen in the transition zone to minimize kinking, but does not provide the advantages of the spring coil to the distal tip of the catheter.